AVAssetExportSession导出需要很多时间

Question

My goal is to let user select video from photos and then let him to add labels over it.

Here is what I've got:

let audioAsset = AVURLAsset(url: selectedVideoURL)
let videoAsset = AVURLAsset(url: selectedVideoURL)
let mixComposition = AVMutableComposition()
let compositionVideoTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeVideo, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
let compositionAudioTrack = mixComposition.addMutableTrack(withMediaType: AVMediaTypeAudio, preferredTrackID: Int32(kCMPersistentTrackID_Invalid))
let clipVideoTrack = videoAsset.tracks(withMediaType: AVMediaTypeVideo)[0]
let clipAudioTrack = audioAsset.tracks(withMediaType: AVMediaTypeAudio)[0]
do {
    try compositionVideoTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, videoAsset.duration), of: clipVideoTrack, at: kCMTimeZero)
    try compositionAudioTrack.insertTimeRange(CMTimeRangeMake(kCMTimeZero, audioAsset.duration), of: clipAudioTrack, at: kCMTimeZero)
    compositionVideoTrack.preferredTransform = clipVideoTrack.preferredTransform
} catch {
    print(error)
}
var videoSize = clipVideoTrack.naturalSize
if isVideoPortrait(asset: videoAsset) {
    videoSize = CGSize(width: videoSize.height, height: videoSize.width)
}
let parentLayer = CALayer()
let videoLayer = CALayer()
parentLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
videoLayer.frame = CGRect(x: 0, y: 0, width: videoSize.width, height: videoSize.height)
parentLayer.addSublayer(videoLayer)

// adding label
let helloLabelLayer = CATextLayer()
helloLabelLayer.string = "Hello"
helloLabelLayer.font = "Signika-Semibold" as CFTypeRef?
helloLabelLayer.fontSize = 30.0
helloLabelLayer.contentsScale = mainScreen.scale
helloLabelLayer.alignmentMode = kCAAlignmentNatural
helloLabelLayer.frame = CGRect(x: 0.0, y: 0.0, width: 100.0, height: 50.0)
parentLayer.addSublayer(helloLabelLayer)

// creating composition
let videoComp = AVMutableVideoComposition()
videoComp.renderSize = videoSize
videoComp.frameDuration = CMTimeMake(1, 30)
videoComp.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer)

let instruction = AVMutableVideoCompositionInstruction()
instruction.timeRange = CMTimeRangeMake(kCMTimeZero, mixComposition.duration)
let layerInstruction = videoCompositionInstructionForTrack(track: compositionVideoTrack, asset: videoAsset)
instruction.layerInstructions = [layerInstruction]
videoComp.instructions = [instruction]
if let assetExport = AVAssetExportSession(asset: mixComposition, presetName: AVAssetExportPreset640x480) {
    let filename = NSTemporaryDirectory().appending("video.mov")

    if FileManager.default.fileExists(atPath: filename) {
    do {
        try FileManager.default.removeItem(atPath: filename)
    } catch {
        print(error)
    }
}

let url = URL(fileURLWithPath: filename)
assetExport.outputURL = url
assetExport.outputFileType = AVFileTypeMPEG4
assetExport.videoComposition = videoComp
print(NSDate().timeIntervalSince1970)
assetExport.exportAsynchronously {
    print(NSDate().timeIntervalSince1970)
    let library = ALAssetsLibrary()
    library.writeVideoAtPath(toSavedPhotosAlbum: url, completionBlock: {
        (url, error) in
        switch assetExport.status {
            case AVAssetExportSessionStatus.failed:
                p("failed \(assetExport.error)")
            case AVAssetExportSessionStatus.cancelled:
                p("cancelled \(assetExport.error)")
            default:
                p("complete")
                p(NSDate().timeIntervalSince1970)
                if FileManager.default.fileExists(atPath: filename) {
                    do {
                        try FileManager.default.removeItem(atPath: filename)
                    } catch {
                        p(error)
                    }
                }
                print("Exported")                                    
        }
    })
}

Implementation of isVideoPortrait function:

func isVideoPortrait(asset: AVAsset) -> Bool {
    var isPortrait = false
    let tracks = asset.tracks(withMediaType: AVMediaTypeVideo)
    if tracks.count > 0 {
        let videoTrack = tracks[0]
        let t = videoTrack.preferredTransform
        if t.a == 0 && t.b == 1.0 && t.c == -1.0 && t.d == 0 {
            isPortrait = true
        }
        if t.a == 0 && t.b == -1.0 && t.c == 1.0 && t.d == 0 {
            isPortrait = true
        }
        if t.a == 1.0 && t.b == 0 && t.c == 0 && t.d == 1.0 {
            isPortrait = false
        }
        if t.a == -1.0 && t.b == 0 && t.c == 0 && t.d == -1.0 {
            isPortrait = false
        }
    }
    return isPortrait
}

And the last function for video composition layer instruction :

func videoCompositionInstructionForTrack(track: AVCompositionTrack, asset: AVAsset) -> AVMutableVideoCompositionLayerInstruction {
    let instruction = AVMutableVideoCompositionLayerInstruction(assetTrack: track)
    let assetTrack = asset.tracks(withMediaType: AVMediaTypeVideo)[0]
    let transform = assetTrack.preferredTransform
    instruction.setTransform(transform, at: kCMTimeZero)
    return instruction
}

The code works well, output video has label, but if I select 1 minute video, export takes 28 seconds.

I've search for it and tried to remove layerInsctuction transform, but no effect.

Tried to add: assetExport.shouldOptimizeForNetworkUse = false no effect either.

Also, tried to set AVAssetExportPresetPassthrough for AVAssetExportSession , in this case video exports with 1 second but labels have gone.

Any help would be appreciated, because I'm in stuck. Thanks for your time.

Answer 1

This is not directly relevant to your question, but your code here is backwards:

assetExport.exportAsynchronously {
    let library = ALAssetsLibrary()
    library.writeVideoAtPath(toSavedPhotosAlbum: url, completionBlock: {
        switch assetExport.status {

No no no. First you complete the asset export. Then you can copy again to somewhere else if that's what you want to do. So this needs to go like this:

assetExport.exportAsynchronously {
    switch assetExport.status {
    case .completed:
        let library = ALAssetsLibrary()
        library.writeVideoAtPath...

Other comments:

• ALAssetsLibrary is dead. This is not the way to copy into the user's photo library. Use Photo framework.

• Your original code is very odd, because there are a lot of other cases you are not testing for. You are just assuming that default means .completed . That's dangerous.

Answer 2

The only way I can think of is to reduce the quality via the bit rate and resolution.

This is done through a dictionary applied to the videoSettings of the AssetExporter, for this to work I had to use a Framework called SDAVAssetExportSession

Then by changing the videoSettings I could play with the quality to get an optimal quality / speed.

    let compression = [AVVideoAverageBitRateKey : 2097152(DESIRED_BITRATE),AVVideoProfileLevelKey : AVVideoProfileLevelH264BaselineAutoLevel]

    let videoSettings = [AVVideoCodecKey : AVVideoCodecH264, AVVideoWidthKey : maxWidth, AVVideoHeightKey : maxHeight, AVVideoCompressionPropertiesKey:compression]

This was the only way I could speed things up.